DESCRIPTION: The long-term objective of this project is to identify the pattern of age-related change and constancy in the functioning of neural systems mediating cognitive abilities. Positron emission tomography (PET) will be used to measure changes in regional cerebral blood flow (rCBF) during subjects' performance of specific cognitive tasks. The general hypothesis to be tested is that rCBF activation, as defined by the pattern of change in the PET voxel map between two task conditions, will be significantly lower and less regionally specific for older adults than for young adults. For each subject, the PET images will be registered to MRI. The project is designed to provide new data regarding the age-related changes in neural functioning that occur independently of the presence of significant disease.